This invention relates to an engine control and sensor for an engine control and more particularly to an exhaust back pressure effect control and sensor.
It is known that the performance of an internal combustion engine can be significantly affected by the tuning of the exhaust system. If the exhaust system is properly tuned, the pulses which emanate back from the discharge end of the exhaust pipe to the exhaust ports can be tuned so as to occur at an appropriate time so as to improve the engine performance. One way this can be done is by utilizing the pulse back effect to cause any fresh fuel air charge which may have passed out of the exhaust port due to overlap conditions to be forced back into the combustion chamber. This improves the charging efficiency and in effect gives rise to a characteristic known as "exhaust supercharging." That is, the pressure in the combustion chamber can be raised above atmospheric in this manner.
A wide variety of methods and apparatus may be employed for achieving this effect and for varying the effect during the running of the engine. This can be done by placing reflective control valves in the exhaust system, changing the effective length of the exhaust system, adding variable tuning chambers, changing the port opening timing for the engine during its running, and/or changing the time of initiation of combustion in the combustion chamber. These techniques are particularly effective in two cycle engines, but the same concept can be employed with four cycle engines.
This effect can be generated with single cylinder engines, as well as multiple cylinder engines. When functioning in conjunction with multiple cylinder engines, even greater effects can be obtained at times. That is, the exhaust pulses from one cylinder may be utilized to influence the combustion chamber conditions in another cylinder through this pulse back effect if a common exhaust outlet is shared by the cylinders.
It has been found that one accurate measurement that is useful in controlling the pulse back effect is by measuring the temperature of the exhaust gasses. By measuring the exhaust gas temperature, it is possible to obtain the desired condition in the combustion chamber through the manipulation of the pulse back effect through the aforenoted methods and other methods which may be utilized to achieve the same result. Exhaust gas temperature affects the velocity of the pulse in the exhaust pipe.
However, it is important that the sensor that is utilized does not actually sense the direct temperature of the exhaust gasses. There is a number of reasons for this. First, the exhaust gas temperature fluctuates quite widely and if the actual instantaneous exhaust gas temperature were measured, there would be wide fluctuations in the control and uneven engine performance would result.
It has been proposed therefore to utilize a sensor that senses the average exhaust gas temperature by measuring the temperature in the exhaust pipe and specifically measuring the wall temperature of the exhaust pipe. This temperature also accurately reflects the actual exhaust gas temperature but the pipe temperature does not fluctuate as widely as the actual exhaust gas temperature does. As a result, more stable control can be obtained and the control is in fact more accurate.
The exhaust pipe walls, however, do not themselves necessarily maintain a constant or representative temperature at all places. For example, in many engine applications, the exhaust port is served by an exhaust pipe which must curve in order to clear the engine and other components to connect to the remainder of the exhaust system. Frequently the configuration of the exhaust system frequently results in the formation of a number of curves or bends. It has been discovered in conjunction with one feature of the invention that the actual positioning of the sensor element in the wall of the exhaust system is significant in the system performance, particularly if the sensor is mounted in a place where the exhaust system curves.
If the sensor is positioned in or near a curve in the exhaust system the exhaust flow may directly impinge on the sensor. In such cases the sensor will be sensing, at least partially, the gas temperature rather than the wall temperature. Hence, the control may become erratic.
It is therefore a principal object of this invention to provide an improved exhaust sensor for an engine that will provide an accurate and stable exhaust temperature signals.
It is a further object of this invention to provide an improved exhaust sensor placement arrangement for an engine exhaust effect control wherein the sensor will provide good and accurate sensor information.
In addition to the importance of having the sensor element be positioned in the appropriate portion of the wall of the exhaust system, other aspects of the sensor are also important in conjunction with its accuracy.
Basically, the temperature sensors comprise a sensor element end that is mounted in contact with the appropriate portion of the exhaust system wall and a terminal end from which the signal is transmitted to the control system. Obviously, the terminal end must extend outwardly from the exhaust system.
This condition gives rise to other problems that may affect the accuracy of the control. For example, in many forms of vehicle application, the sensor element may be disposed in direct or close contact with the atmosphere. Such things as rain, moisture or changes in ambient temperature can therefore affect the accuracy of the sensor. That is, if the terminal end is at a substantially different temperature from the sensor end and/or if the temperature at the terminal end fluctuates widely, then the accuracy of the sensor can be compromised.
In addition to this problem, if the terminal end is disposed in an outwardly protruding position, there is always the danger that it may be struck by a foreign object or inadvertently struck and damaged.
It is, therefore, a further object of this invention to provide an exhaust temperature sensor mounting arrangement for an engine control wherein the terminal end is disposed so as to avoid the aforenoted problems.
It is, therefore, the principal object of this invention to provide an improved and highly accurate exhaust system temperature sensor for an internal combustion engine wherein accurate and representative signals can be generated and transmitted to the control with accuracy.